The present invention relates to a class of new silane-substituted cycloalkene compounds that are an innocuous, air-stable liquid. These silane-substituted cycloalkene compounds can then, for example, be thermally decomposed to yield high purity silane for point-of-use application in the semiconductor industry.
Many industries use pyrophoric gases for a variety of processes and operations. In the semiconductor industry, a variety of pyrophoric gases are used during the manufacture of semiconductor devices. These gases are termed pyrophoric due to their ability to ignite spontaneously upon contact with an oxidant such as oxygen. Thus, these gases may ignite upon contact with air, and if a pocket of pyrophoric gas contacts air, an explosion may result. The possibility of explosion is increased by the tendency of some pyrophoric gases to “self-protect”, wherein bubbles or pockets of the pyrophoric gas develop which prevents reaction or neutralization of the pyrophoric gas in a controlled manner.
Pyrophoric gases are usually used for the deposition of various layers or for introducing dopants into the various layers of a semiconductor device. For example, silane (SiH4) may be used along with oxygen to from a silicon dioxide (SiO2) layer in a chemical vapor deposition (CVD) system. Diborane (B2H6), phosphine (PH3), and arsine (AsH3) may be used to add dopants to a layer. Silane also is used to form polycrystalline silicon layers as well as epitaxial, single crystal silicon in a variety of processes. Silane gas is an inherently dangerous material in that it is highly volatile and pyrophoric (i.e., it explodes on contact with air). A recent SEMATECH report indicated that on-site accidents involving silane cost the industry over $500K/year (See, e.g., SEMATECH Technology Transfer Report #94062405A-ENG, Silane Safety Improvement Project S71, 1997); and indirect costs (e.g., safety restrictions during transportation and storage, loss of production due to silane-related incidents, etc.) are likely much higher.
U.S. Pat. No. 6,103,942 discloses a method of preparing high purity silane. The process comprises a temperature assisted reaction of metallurgical silicon with alcohol in the presence of a catalyst. Alkoxysilanes formed in the silicon-alcohol reaction are separated from other products and purified. Simultaneous reduction and oxidation of alcoxysilanes produces gaseous silane and liquid secondary products including the active part of a catalyst, tetra-alkoxysilanes, and impurity compounds with silicone-hydrogen bonds. Silane is purified by an impurity adsorption technique.
Another technique for producing high purity silane is described in U.S. Pat. No. 4,676,967. The overall process includes (1) the enhanced production of trichlorosilane from metallurgical silicon and hydrogen, (2) the disproportionation of trichlorosilane to produce high purity silane, and (3) the conversion of said silane to high purity silicon, if desired. The disclosure of all of the above patents and of all other articles and patents cited herein are incorporated herein by reference as if fully set forth herein.
What is needed in the art is a process for making a silane gas precursor which is innocuous and air stable that can be easily and directly decomposed to high purity silane gas for point-of-use in various industrial applications.